Technical Field
The present disclosure relates to a wire bonding method and a wire bonding structure.
Description of Related Art
A semiconductor die is a small integrated circuit formed on a semiconductor wafer. The die is cut from the wafer and then attached to a substrate or semiconductor chip carrier. Bonding pads on the semiconductor die are electrically connected to electrical contacts on the carrier (also known as leads or lead fingers) using bond wires with wire bonding equipment. Wire bonding is a solid phase process that uses a combination of heat, pressure and ultrasonic energy to form a connection between a bond wire and the bonding pads and carrier leads.
As shown in FIG. 1, in semiconductor device assembly of wire bond type devices, a first, ball bond 110 is typically used to attach a tip of the wire 100 to a bonding pad 200 on the die. The ball bond 110 is formed by applying a high voltage electrical charge to the tip of the wire 100, which melts the tip such that a ball is formed at the tip. The ball bond 110 is then welded to the bonding pad 200. The wire 100 is then moved to one of the leads of the carrier and a second bond is formed to attach the other end of the wire 100 to the lead of the chip carrier.
During the bonding, the ball is firstly pressed onto the bonding pad 200 on the die, so that the ball is deformed to increase the contacting area between the ball and the bonding pad 200 before being welded. Once a predetermined force with which the ball is pressed onto the bonding pad is satisfied, an ultrasonic energy is applied to heat and melt the contacting interface of the deformed ball (i.e., the ball bond 110) and the bonding pad 200. After the molten contacting interface is cooled, the ball bond 110 and the bonding pad 200 are welded.
However, if the hardness of the wire 100 is greater than that of the bonding pad 200, the ball bond 110 will sink into the bonding pad 200 and the bonding pad 200 will correspondingly splash during the pressing of the ball bond 110 onto the bonding pad 200 and/or the applying of the ultrasonic energy. Once the thickness of the bonding pad 200 is too thin, the pressing and/or the applying may easily damage the die (e.g., produce cracks), which may further affect the interconnection structures and thus cause abnormal electrical signals. That is, the thin bonding pad 200 cannot provide a cushioning effect to the die. To solve the problem, the thickness of the bonding pad 200 can be increased, but the cost is also increased.
Accordingly, how to provide a wire bonding method to solve the aforementioned problems becomes an important issue to be solved by those in the industry.